1. Field of the Invention
The present invention generally relates to a bearing assembly of a kind whose temperature needs to be monitored and, more particularly, to the bearing assembly having a temperature sensor built therein, suitable for use in, for example, wheel bearings and shaft bearings used in railway vehicles.
2. Description of the Prior Art
In shaft bearing assemblies employed in railway vehicles, one or more temperature sensors which are a member separate from the bearing assembly are incorporated in a housing for the bearing assembly for detection of the temperature of a surface of the housing so that an abnormal temperature evolved in the bearing assembly can be detected.
It has, however, been found that with the sensor-equipped bearing assembly now in use, the following problems have been involved:    (1) Since the temperature sensor used therein does not detect the temperature of the bearing assembly directly, the timing at which the abnormal temperature is detected tends to be retarded, resulting in that at the time of actual detection of the abnormal temperature, the bearing assembly would have already damaged detrimentally. Once this occurs, determination of a cause of the abnormal temperature would be virtually futile.    (2) Since the temperature sensor is a member separate from the bearing assembly, a space for installation thereof is required within a limited space available in the bearing assembly.    (3) Because of the temperature sensor being a member separate from the bearing assembly, the number of component parts in the bearing assembly as a whole tends to increase, resulting in complicated and time-consuming servicing operations. While it is a general practice to replace the bearing assembly regularly during a cycle checkout, replacement of the temperature sensor is also required separate from and independently of the replacement of the bearing assembly and, accordingly, complicated and time-consuming procedures are required in performing a job of replacement.    (4) Considering that the temperature sensor is secured to an outside of a bearing box forming a part of the bearing assembly, the temperature sensor is susceptible to damage or malfunctioning by collision with scattered stones and/or rocks, resulting in false generation of an erroneous signal indicative of detection of the abnormal temperature.
Also, the prior art wheel bearing assembly used in railway vehicles has been well known, in which as shown in FIG. 8, a temperature sensor 63 in the form of a thermocouple or the like is disposed on one end face of an inner race 52 that forms a stationary bearing ring. An outer race 53 of the wheel bearing assembly is positioned radially outwardly of the inner race 52 with rolling elements interposed therebetween and has its outer peripheral surface secured to a corresponding wheel (not shown) while forming a rotatable bearing ring.
The prior art wheel bearing assembly shown in FIG. 8 is effective to directly measure the temperature of the bearing assembly itself. However, since the temperature sensor 63 is designed to be carried by the inner race which is one of the bearing rings forming the bearing assembly, mounting of the temperature sensor on the inner race is difficult to achieve, resulting in reduction in productivity.